1. Field of the Invention
The present invention relates to an inkjet printing apparatus and an inkjet printing method.
2. Description of the Related Art
In an inkjet printer, main droplets of ink are ejected from ink ejection ports of a printing head to be landed on a sheet, and in addition thereto, small droplets of ink separated from the main droplets of the ink forming the main droplets are landed on the sheet to form small dots thereon. This small dot is called “satellite”. The small droplet forming this satellite is originally ejected together with the main droplet and is formed in such a manner that a tail portion of the main droplet is generated at the back side by tension between the main droplet and a liquid surface of meniscus of an ink ejection bore and is separated from the main droplet for being in a spherical shape with surface tension. In consequence, the small droplet forming the satellite is, as compared to the main droplet, thought to be subjected to more backward forces by surface tension at the time the small dot is pulled away from the meniscus of the ink ejection bore, and an ejection speed of the small droplet is slower than that of the main droplet. Since the main droplet ejected from a large-droplet nozzle array for ejecting relatively large ink droplets has a large dot diameter, the satellite having a slow ejection speed is landed to overlap over the main droplet on a sheet at the time it is landed thereon. On the other hand, since the main droplet ejected from a small-droplet nozzle array for ejecting relatively small ink droplets has a relatively small dot diameter, the satellite having a slow ejection speed is landed away from the main droplet on a sheet at the time it is landed thereon. In this way, since the satellites form dots which are not intended originally, many proposals have been made as technologies for restricting the satellite (for example, refer to Japanese Patent Laid-Open No. 2007-118300), but it is difficult to restrict occurrence of the satellite.
In a printer using the printing head provided with large-droplet nozzle arrays for ejecting relatively large ink droplets and small-droplet nozzle arrays for ejecting relatively small ink droplets, the satellite of the small-droplet nozzle array is landed away from the main droplet as described above. Since the satellite generated in such a printing head has relatively low kinetic energy, a landing position of the satellite to the main ink droplet is disturbed by the self-current generated by ejection of the ink droplet and the flowing current generated by transfer of a carriage. The disturbance in the landing position of the satellite generates density variations to cause image quality to be degraded.
An object of the present invention is to provide a printing apparatus and a printing method capable of suppressing degradation of image quality due to disturbance in landing positions of satellites.